Greenpeace activists staged a mock fumigation outside EU offices Wednesday to warn off the European Commission from authorising new genetically modified (GM) crops.

Turned out in yellow protective gear, 27 activists -- one for each of the European Union states -- warned that planting new GM varieties would cause a dramatic increase in herbicide use and sprayed a banner saying "GM crops = more agrochemicals".

Greenpeace cited a study saying the cultivation of new GM crops would increase herbicide use by up to 15 times.

The Commission is considering authorising 26 new GM crops, 19 of them genetically modified to be tolerant to herbicides -- mostly glyphosate, which is an ingredient of Roundup, a weedkiller produced by US agricultural biotech company Monsanto.